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Prevention of low blood sugar in insulin therapy

Identifying normal situations that may result in low blood sugar enables you to prepare for them.

Blood sugar can easily drop too low in insulin therapy because various insulin products behave in a characteristically formulaic way, regardless of the blood sugar level. It is important to know the effect of the insulin products you use: how soon is the onset of effect, when does it peak and how long does it last? In addition, increasing an individual insulin dose increases the product’s duration of action. If the injection site is swollen or hardened, the absorption of insulin is reduced and the onset of action slows down.

Low blood sugar can be anticipated and prevented

  • If your blood sugar repeatedly drops too low at night and before meals, in all likelihood, it is necessary to reduce the basal insulin dose. If you take your basal insulin in two divided doses, primarily reduce the dose that corresponds to the time when low blood sugar episodes occur. For instance, if the lows happen during the night, reduce your evening dose; if they occur during the day, reduce your morning dose.

  • If your blood sugar repeatedly drops too low within 2–3 hours of a specific meal and after a bolus insulin injection, the amount of bolus insulin is probably too high compared with the amount of carbohydrates in the food.

  • If you only take the bolus insulin at the end of or after a meal, the blood sugar level often increases too much and can then drop too low 3–4 hours after the meal. Whenever possible, you should take bolus insulin 10–20 minutes before eating.

  • If you are doing exercise within two hours of taking bolus insulin when its action peaks, you should reduce the pre-meal dose by 30%–50%.

  • If you have had a physically active day, you should reduce the bedtime insulin dose by 10%–20%.

  • If your blood sugar level is below 6 mmol/l when you go to bed, you should have a small snack with 10–20 g of slow-acting carbohydrates.

  • If you consume alcohol, ensure adequate carbohydrate intake and consider reducing your insulin dose for the following night. Monitor your blood sugar levels more frequently than usual during alcohol consumption and in the following 24 hours.

Updated 30.9.2023